Irrigation has been practiced in one form or another for a great many years. The average home owner has a lawn, some trees and shrubs, and perhaps a garden, and in those areas where the annual rainfall is insufficient to maintain vegetation, he is obliged to provide some form of irrigation. This is usually accomplished by means of a portable water hose attached to the city water lines, which convey the water to the point of useage, and a sprinkler system, spraying nozzle, or other outlet which distributes the water over an area. Usually it is necessary to move the water hose and distributing outlets about, quite frequently, in order to cover an area of any size.
Another form of irrigation system that is frequently used in maintaining large lawns is a network of fixed sprinkling or spraying outlets which are connected to the water supply by means of underground pipe. This form of irrigation, as all similar ones presently in use, sprays the water over the surface and wastes a good part of it on plant foliage, improper distribution and subsequent evaporation.
Still another form of large-scale irrigation that is used in arid, or semi-arid climates, where agricultural crops are raised for profit, is that of the canal, ditch, furrow and dike. Permanent canals convey the water from the storage dam to the land being irrigated and a system of ditches and furrows adjoining the canal distributes the water over the surface and thence to the crop being raised. Alternatively, the area is divided by a system of dikes which allows an entire area to be flooded.
To avoid excessive loss of water by evaporation where row crops are raised, the system of irrigating furrows is usually destroyed a day or two after irrigation and the surface between rows cultivated; i.e., pulverized to inhibit the flow of water between earth particles adjacent the surface and whence the evaporation. A few days following this, depending upon the climate, the area must again be furrowed, and following this, again irrigated, and the foregoing sequence of events repeated every week or ten days throughout the growing season.
Today, as one travels about farming areas, one sees many overhead sprinkling systems used to irrigate large fields. This type of sprinkling system operates under relatively high water pressures so that a rotating spray from each nozzle covers many square yards of surface; nevertheless, such systems must be moved about considerably to cover an entire acreage that is under cultivation, as well as get the pipe and sprinklers out of the way for other farming operations.
There are, quite naturally, many problems relating to the supply and distribution of water for irrigation. As the population grows throughout the world at a quite rapid rate, the water storage and distribution systems of most municipal supplies usually get overtaxed during the summer months. Quite often, it becomes necessary for municipal services to ration the water or even prohibit its use for irrigation altogether so that water will be available for other more essential services.
Again, the amount of water that can be made available for large scale agriculture depends both upon the rainfall and storage facilities, and these things, in turn, limit the amount of land that can be cultivated in any particular place. Another factor limiting the amount of land available for agriculture is that of topography, and the only lands which can today be irrigated, except for the overhead sprinkling system, are those which are level, or at least nearly level, with gravity controlling the distribution of water during irrigation.